It's always hard knowing what to do on a layover, unless you are lucky enough to be at an airport that has been perfectly designed for travelers. Schiphol Airport in Amsterdam is one such delightful locale, with so much to see and do it makes you want to stay longer. There's plenty of Dutch food (especially the excellent cheese and smoked salmon) and lots of shopping. You can even buy Dutch tulip bulbs to bring home. Massages, showers, sleeping lounges, an oxygen bar, and a tranquil meditation space will also help to ease your transition into a new time zone.
My favorite spot at Schiphol is the small Reichsmuseum gift shop. Not for the shop itself, which does have some delightful Dutch artwork for sale plastered onto mugs, coasters, T-shirts, etc. But, follow the steps up and you will find yourself in a mini-Reichsmuseum exhibit, which changes regularly. Twenty or so paintings hang behind glass, and with so few visitors, you can get up close and personal with these minor masterpieces.